1. Field of the Invention
The present invention relates to a sheet conveying apparatus which conveys a sheet, and an image forming apparatus which is provided with the sheet conveying apparatus.
2. Description of the Related Art
In recent years, when an image forming apparatus such as a printer or a copying machine performs a printing operation, a wide variety of sheets are used depending on purposes. In particular, there has been increasing demand for a thick sheet used in packages made of a boxing material as a wide variety of sheets, but the sheet has a problem in that rigidity is large and sheet clogging easily occurs. Therefore, as a countermeasure, a radius R of a bending portion in a conveying path is made large, resistance exerted from a conveying guide when the sheet is conveyed is reduced, and a nip pressure of a conveying roller is significantly increased to raise a conveying force.
Furthermore, in order to comply with the demand for the wide variety of sheets, space saving of installation area for the apparatus or cost saving is also increasingly demanded. However, when the radius R of the bending portion in the conveying path is made large, the apparatus is increased in size to cause the cost to be significantly increased, so that it conflicts with reality. For this reason, the countermeasures of raising the nip pressure of the conveying roller and increasing the conveying force are widely employed.
In addition, as illustrated in FIGS. 10A and 10B, likewise a driven roller 253 which is on a door side to be opened/closed with respect to a main body of the image forming apparatus, a configuration in which a pressing spring 256 is hooked around and presses a driven roller shaft 252 is employed in many products for the space saving and for the low cost (Japanese Patent Laid-Open No. 06-144633).
However, in the configuration illustrated in FIG. 10B, in a case where the nip pressure of the conveying roller is raised, the length of the pressing spring 256 is not possible to be long, so that a spring constant is increased. In this case, since a partial force f0 is generated in a direction of angle θ0 with respect to in a direction of a pressing force F0, a variation in pressure is easily increased still more. Then, since the pressing force is increased, a roller shaft 215c of a driving roller 215 or an opening/closing guide 221 is significantly bent, an actual length of the pressing spring 256 is reduced at the time of pressing, the spring constant is increased, and a necessary pressing force is also not obtained.
As illustrated in FIG. 10A, in the opening/closing guide 221 where an opening/closing hinge 227 is provided on a side (herein, an inner side) of a width direction perpendicular to the conveying direction of the sheet, bending on the side (the inner side) of the width direction is different from that on the other side (the front side). For this reason, a difference of the pressing force on the inner side and the front side of the width direction is increased, so that the sheet is fed on the skew.